Conventional macroscale methods for separation of cells include physical filtration using membrane-based filter and density gradient centrifugation which exploit differences in cell size, deformability, and density to filter out target cells. These techniques are labor-intensive and require multi-step sample preparations which may introduce artifacts or lead to loss of desired cells. Membrane filtration methods are also easily susceptible to clogging and require frequent cleaning. Further, evidence of mechanical stress-induced changes in original phenotype of target cells subjected to filtration and centrifugation techniques has also been reported. Recently, inertial micro-fluidic devices were explored as a filterless size-based cell fractionation method. See Di Carlo D. Inertial microfluidics. Lab on a chip. 2009; 9(21):3038-46; Kuntaegowdanahalli SS, et al. Lab on a chip. 2009; 9(20):2973-80; Bhagat AAS, et al. Biomedical Microdevices. 2010; 12(2):187-95.
However, there is a continuing need to develop simpler and more efficient techniques to process blood samples that can minimize cell loss and maintain the original target cell phenotype for subsequent analysis.